Art of esterification



Patented Oct. 28, 1947v William Beach Pratt, deceased, late of Boston,

Mass, by Annette Harri Boston, Mass, assi-gnor, to Joseph G. Denny, Jr.

s Pratt, administratrix, by mesn'e assignments,

No Drawing. Application August 8, 1940, Serial No. 351,912

8 Claims. 1 Broadly speaking, this invention relates to es,- terification with organic acids and 'anhydrides, or mixtures of the s'ame, particularly to the esteri fication of cellulose, starch, dextrins and other carbohydrate bodies preferably in their natural or normal state, as individual fibers, granules, fiber aggregates as woven goods, cloth, textiles or twisted or untw-isted rovings and yarn, composed wholly or partially of cellulose.

This invention involves novel procedure and compounds used in the formation of valuable products, and especially applicable wherein the original appearance of the fiber or granule may or may not be materially modified in appearance by transformation into the corresponding ester form, and whereby the toughness, flexibility and elasticity of the esterified carbohydrate in nearly every instance is at least equal to the original body from which the ester has been prepared, especially when the natural carbohydrate is a fiber or filament priortoesterification,

In general, the practice of this invention involves treatment of a single or mixed carbohydrate, as normal, natural cellulose, as distinguished from hydrocellulose, hydrated cellulose, oxycellulose, degraded or otherwise modified normal cellulose, or there may be used a mixture of celluloses with other fibrous bodies, said carbohydrate being in the substantially anhydrous .condition when catalysts, diluents and/or reactants are contacted therewith, and initially treat the same with a body or bodies having catalytic functions, dissolved or suspended in a neutral volatile liquid, which liquid may be an ester or susceptible to esterification in the carbohydrate esterifying bath, to an ester of the same acid radical as the carbohydrate esterified, yet in the esterified condition is usually substantially a non-solvent, or at best a poor solvent of the carbohydrate ester formed. 7

Where cellulose in some form is the carbohydrate to be esterified, it. ispreferred to employ natural or normal cellulose in the fibrous state, as linters, fly, roidngsfstame, woven, sheeted or pressed form, as yarn, cloth or textiles, and from which substantially all atmospheric moisture, has been removed atthe time the cellulose is initially treated.

If woven or textile fibers are to be esterified and with little or no observable change in form, struc ture or appearance during esterification, there may be employed a textile who ly of natural cellulose fibers, or a mixture including mercer-ized or other treated or modifiedrcellulosic fibers, or a mixture of cellulosic natural fibers with other fibers containing nitrogen, as wool or silk.

As catalyst there is employed a body in the liquid or solid state, or a plurality of suitable dissimilar bodies, which are partially or totally soluble in or miscible with an aliphatic hydroxide or hydroxides, or mixture of similar or dissimilar aliphatic hydroxides with aliphatic oxides, and which are substantially anhydrous when used as catalyst solvent or diluent, which comprise in the hydroxide form less than five atoms ofcarbon, or in the oxide form 'lessthan ten carbon atoms, and which are soluble in or partially miscible with water, and are also capable of esterification in the same bath in which.v the carbohydrate is being esterified, but which aliphatic ester when formed is a non-solvent or at best a weak solvent of the esterified carbohydrate, thus permitting said carbohydrate to .be esterifi'ed under normal pressure and tension without appreciable change in physical form or appearance.

Where an aliphatic hydroxide of more than five carbon atoms or the corresponding aliphatic oxide of more than ten carbonatoms are employed alone or admixed with an aliphatic hydroxide, .or oxide of lesser carbon content, in general, less satisfactory results have been obtained.

As aliphatic, hydroxide, oxide or ester, there may be used methylalcohol or ethyl alcohol as examples, either alone or admixed together in various proportions, or with a proportion of the corresponding or other oxide, as diethyl oxide, (Cal-I5) 20, or an alkyl ester of an aliphatic monocarboxylic acid as methyl or ethyl acetates.

Or, there may be used a higher alcohol mixed with a lower one as iso-propyl and methyl alcohol, but it is preferable that the liquid be substantially V anhydrous when catalyst is dissolved therein or mixed therewith and the mixture contacted with the carbohydrate.

As catalyst there may be employed any suitable halogen (except fluorine) oxyacid or anhydride or the same including perchloric acid as set out-in an application of W. B. Pratt, Serial No. 289,712, filed Aug. 11, 1939, or mixtures of halogen oxyaoids of same or dissimilaroxygen content, but preferably of relatively high oxygen content, which is or are miscible with or soluble in the above mentioned aliphatic alcohols; esters or mixtures thereof.

As a specific example of relatively high oxygen content, satisfactory results may be obtained by the use of bromic or perbromic acid, or their anhydrides bromine pentoxide '(br-omic anhyd-ride) or bromine heptoxide. (perbromic 'anhydride) as distinguished from the lower oxyacids, bromous or hypobromous, or their respective anhydrides, and less satisfactory effects result from the use of corresponding oxyacids, containing not less than three oxygen atoms of the halogens bromine and iodine or their corresponding anhydrides, or of chloric acid, alone or in admixture.

According to this invention, best results are obtainable when operating with the carbohydrates in their diiferent variations and forms, by impregnating the carbohydrate with the halogen oxyacid, the selection of most suitable halogen oxyacid catalyst or mixture thereof in esterifying a particular carbohydrate body, depending in a measure upon the nature, source, form and other characteristics in the carbohydrate initially used, and the form and physical properties desired in the finished esterified product.

A catalyst of or containing a major proportion of bromic acid, or a mixture of bromic and iodic acids is desirable.

One preferred method of practice of this invention taking the carbohydrate group as a whole involves impregnating a substantially anhydrous aliphatic monohydric alcohol containing a halogen oxyacid of relatively high oxygen content, as bromic acid in the hydrate form, thus forming a relatively fixed constant boiling acid soluble in the monohydric alcohol, and which is convertible by dehydration into a more or less volatile oxide as bromine pentoxide which appears in general to be more effective as an esterification catalyst than the original halogen hydroxy acid.

The mechanics of this invention appear to be that the impregnation of the carbohydrate with alkyl hydroxide or oxide devoid of water repellents improves the uniformity of the wetting of the carbohydrate by water of reaction subsequently formed in situ therein and places it on the same phase of reaction as a suitable substantially anhydrous dehydrating and esterifying reagent, such as an aliphatic acid anhydride, as acetic anhydride.

The anhydride reacts with the hydrous catalyst to apparently form a volatile and more effective catalyst such perhaps as bromine pentoxide; reacts with the alcohol to form water and a diluent of the anhydride used to esterify the alcohol to the corresponding ester; and reacts rapidly and uniformly upon the activated carbo- I hydrate to form an ester, as acetylcellulose.

The catalyst thus formed in situ, or in the nascent state as it were, in the carbohydrate is unstable in the presence of an oxidant or oxidizable material such as cellulose, and is stabilized during esterification of the carbohydrate and thereafter removed from the formed ester as by an evaporative step, thereby preventing degeneration and hence requiring little or no washing.

The stabilization of the relatively unstable catalyst is preferably effected by maintaining air or other source of oxygen in contact therewith, for a portion of the time, or throughout the esterification phase.

The principal of this invention is intimately connected with the relative amounts and distributicn of water, and minimum amounts of water in each of the entering components, and in each phase of the treatment of carbohydate initially until the close of the esterification step. There should be some moisture present to initiate esterification, after which sufiicient water is obtained by Virtue of hydroxyl in the alcohol and the hydroxyl in the carbohydrate incident to acetation or other form of esterification with qrga iq acids or anhydrides or both. The moisture originally present in the carbohydrate just prior to initiation of esterification and which preferab y should be less than one percent as determined by dehydrating at 105-ll0 0., coupled with the relatively small amount of water in the catalytic body as initially introduced into contact with the cellulose, may supply the water to initiate esterification of the alcohol under the conditions prevailing, and this amount of water is usually deemed sufficient, due to the increased receptivity, and increased uniformity of receptivity of the carbohydrate for esterification reaction, by virtue of the commingling of catalyst and carbohydrate under the conditions herein set forth.

Esterification is greatly facilitated, accelerated and rendered more uniform by Virtue of the presence of the halogen oxyacid anhydride as bromine pentoxide, as inducing and continuing esterification under the conditions prevailing. Such bromine pentoxide has no apparent inju ious effects, due primarily to its proneness to evaporate and completely volatilize from the treated carbohydrate at the close of the esterification. The presence therein of the neutral, volatile, cellulose ester diluent in ester form, also modifies and lessens danger of untoward effect upon carbohydrate at the initial point of esterification, and during the esterifying cycle.

The bromine pentoxide is preferably formed in situ and is preferably effected by the reaction of an esterifying anhydride on a bromic acid hydrate containing a proportion of moisture, say of 60% to absolute HBlOs, and about two molecules of water, and which is capable of holding 1-1.5 additional molecules of water.

Such bromic acid hydrate appears to be stable to light and mechanical shock; is soluble in or miscible with the aliphatic alcohols or esters mentioned herein, and has a relatively low boiling point. It therefore will not vaporize from the cellulose or fabric to any considerable extent under the conditions to which the fabric is treated prior to esterification.

For purposes of description, thisinvention may be said to involve two steps, both carried out with substantially anhydrous materials as expressed in percentage of the combined reactants, and as follows:

(1) Treatment of carbohydrate prior to esterification with catalyst associated with alkyl hydroxide, with or without alkyl acetate.

(2) Contacting treated carbohydrate ester-forming components.

(1) Preliminary treatment of carbohydrate. For purposes of illustration only, one exemplification of this process will be described as of treatment of normal cellulose in the fibrous form and in the textile condition, as muslin, linen, duck, drill, canvas or other form, weight, weave or weft or suitably purified cellulose fiber.

The catalyst selected is first dissolved or suspended in the proportion desired in the alkyl hydroxide or ester or mixture thereof, or mixture of alkyl hydroxides, with or without the addition of an alkyl ester thereto, all in the substantially anhydrous condition. 7

Synthetic methanol alone or with a proportion of ethyl ether, or absolute ethanol, in general has been found preferable, especially when a fibrous carbohydrate carboxylate is to be the finished ester.

If upon contact of catalyst with alkyl hydroxide, too much heat is evolved as the result, the mixture may be cooled before use. or the alkyl with subsequent 3 The removal of the practically all free or originally uncombined water, including physically attached or chemically combined water (so-called water or constitution) from the carbohydrate, as cellulose, and the complete and uniform impregnation-of its molecular structure with anhydrous aliphatic hydroxide, places the cellulose in the same phase or zone of reaction as the water-free esterifyin'g bath. originally contained small amounts of water, the probability is that it would first be combined with the acid anhydride to form the corresponding acid.

--By thus eliminating any interfacial tension between the constituents of the esterifying bath and :the products to be esterified, the latter are completely, uniformly and substantially instantaneously penetrated and impregnated by the former, so that the esterifying reaction proceeds uniformly under these conditions throughout the molecular cellulosic' structure.

By thus observing the prior outlined conditions, this permits of substantially instantaneous esterification perfectly uniform throughout, and hence with no observable appreciable degradation of cellulose in passing from the normal into the ester form, thereby assuring that the cellulose ester so formed shall retain its. original desirable physical characteristics as tensile strength "not only substantially unimpaired, but appreciably augmented, sometimes up to50% increase and more.

This includes toughness, elasticity, flexibility; resiliency, tensile strength and uniformity of gelatlnization, colloidation and solution in a wide variety of solvents, solvent combinations, diluents,-fiexilizers, plasticizers and supple-inducing bodies: I

, 'Such acetated celluloses in the fabric form possess the desirable qualities to a much greater degree than doyarns and fabrics made from or con taining hydrolyzed, degenerated or oxidized cel lulose, either before orafter esterification thereof.

The esterification of celluloses according to this invention, especially afterthe cellulose filaments have been spun into yarn or woven into fabric, results in an increase in diameter of the individual filament, an increase in number of turns or twists per inch in the yarn, and the relative transparency, translucency, opacity, luster and other properties of such acetated yarns or,

fabrics made therefrom, may be largely modified and controlled by the degree of tension applied thereto in one or more directions during the esterification and subsequent treatments and usually until the finished fabric has assumed the airdry condition. 7 V

The weight of the carbohydrate is also increased incident to acetation by this invention, up to 50%, and even more.

After contact of catalyst and cellulose in the presence of an aliphatic hydroxide or oxide or mixture thereof, or a body possessing alcoholic functions, for the length of time required to assure complete and uniform association and permeation of catalyst of the nature as herein disclosed with and into the cellulose, either at rest or with agitation, excess of liquid and catalyst is removed in any convenient manner, as by pressure, centrifugalization or evaporation, and until the original cellulose shows a gain in weight of not to exceed about 30%, when it is immediately, or after maturingcontacted witnesterifying components. 7

(2) Esterification of preliminary treated cellu- Even if the esterfying path prior pretreatment step, after that alcohol or.

ether is subjected to esterification.

If acetation of cellulose is desired and ethanol has been used as the vehicle to contact cellulose and catalyst, then the esterifying bath is preferably composed of or contains the aliphatic acid anhydride as acetic anhydride, with ethyl acetate as non-solvent or diluent for the acetated cellulose formed.

If the ethanol above has been replaced by a mixture of ethanol and ethyl acetate or methanol and methyl acetate, then the esterifying bath'diluent may be either methyl acetate, ethyl acetate or a mixture of the same in the desired proportions.

If the processis to be a more or less continuous one as where rolls of textiles are to be esterified, then the textile is preferably placed under tension, either or both longitudinal or lateral, the degree of tension employed in either or both-directions being determined by the properties desired in theesterified textile. Cotton or linen textile, or a mixture of mercerized andnon-mercerized cotton fibers undergo considerable contraction upon being esterified in accordance with this invention, The stresses on the textiles are preferably gradually decreased during the early stages of esterification and gradually increased during the later stages of esterification by varying the tension applied to the textile.

Where relatively considerable tension is employed, it has been found that certain physical properties as luster are profoundly modified, esterification proceeding more speedily and uniformly when considerable tension is applied to the fabric, perhaps due to more. readily penetration 'in the textile of esterifying agent in the stretched condition.

Esterification of carbohydrates, particularly cellulose and readily noticeable in the fabric form, causes a distinct tautening and contraction, and variation in tension or degree of tension imposed during the esterifying step, produces corresponding results in appearance of the finished product, especially in augmentation of the sheen, feel and facility of penetration of dyestuif and other treating materials normally applied to cellulose goods,v

Aftercontact of e'sterifying liquid with cellulose for the period required to produce the degree of esterification desired, and preferably in the presence of a source of oxygen, fabric is removed f 2,429,644 x acid, or mixtur thereof, where a mixed earn) this invention into effect am; a applied to hydrate esteris to be produced. 'euulose asthf 10' rate in the non-woven This method perm ts, the use of amounts of ve'ondition, the dell linters properly purl; est'erifying acids or 'anhydr des in such slight qi n'gnny drier by excess of the amounts theoretically required for :3 in and until the reaction with the alcohol or aloohol and. ether 10w 1%, allowed and with the cellulose, that uniform mono-, dif and tri-e'ste'rs of 'celluld broadly speaking, may be directly produce Properly pr portion n g h theamount of the rifylngahhydride o acid or both, to the alcohol janaeeumos and control of the temperature an other constamps, during este'rification, ther b avdidiriie o' minimizing necessity for hydrolyzit g or slapbfr yili'g primary ester to 's' ondaiy e'ste'r, unlessso desired Factors govern "g the percentages oiacetje anhydride usually necessary for the flirmation of a desired primary or secondary ulo's'e acetate, the reactions involved, and eontr 's desirable in commercial practi'ce 'are illustrated by the fol-- lowing table applijgable tothe introduction into acetic anhydride of 100 pound of cellulose cond w hanh rus A '2 he w g f e olyd catalyst is made to ated temperature, and

agitated for several o ellulo e and catalyst is 'ma'in 11 a 5d ton in r to We 15 n of 'atm'ospheric osionefe has been ge taining 30% methanol and catalyst ,as erein: x I t yt o" be imparted to Before set forth: 7 the cellulose Iv; Pounds of water foiined 8.46 l g- 9, F ii i Pm Pounds of methyl acetate formed 69.3 g ti g or Pounds of 109% acetic 'anhydride hydrolyzed by the Water formed-. 48.0 Pounds of acetic acid formed from the hydrolysis of the acetic anhydride 56.4

13 .fo in c u o rtria t e (based o a 106 cellulose molecule) under such conditions; there theoretically should he initially present not less than 293 pounds of acetic anhydrlde; or to form cellulose diacetate there should be'init iall-y present not less than 227.3 :pounds ofacetic anhydride; or to form gamma rnonoacetate there should be initially present not less than 161.6 pounds of .jactib ail llydiiide.

In ,comm rein praf ticeit advantageous to use aphroximately 101%, are in excess of -the amounts of acetic anhyd e theoretically indicated, but this amount is "usceptible t 0911- 'siderable Variationdepehii (g :llbonfthecondition and nature of gthe carbo' area at the t m esterifi'ca'tionfthe texnperatliie bl estrifi cation, and the particular Halo en hydroiky acid used asjcatalySt. we .v V

The uniform size nation of fibers with such 's'inan amounts of anhydr'ide is difficult, hence it is generally desirable addto thanhydri de a suflicient quantity or .dilu .to initiate, {facilitate, control and if Whenthecellulose is simply "as ed t gh. the ,este'rifieatlonbath andthe re ct 'bletea during the Inoyeinent of the 'c' lulose through the-air, "much less diluent is, r," ui dtnan w en th eenumse iseornpletely'es edinothebath. I, When it is 951 Ed 126 ,rorma ,ceumojse ester" in 'solutionrather thanfmaintaginthe structural I H identity ofthe"fibers,; the diluntmay compr se tQ Z Y-PY W or contain a solvents torqthe par'tioular cellulose 5 v acetate being .forrned, jas fo'r ,instanc e, acetic D acid'may'lo'e useea diluent whencellul 'e' e; tate in solution mine esterizingvbaith s o h d 901 .01 .mai' tb' li t ior r i tei1ity constants I any case tne mt -b i 9 92y, vusually by both ions, and dried at a.

ec -1 yoi ehu yr pommrce ,is ture, and Wetted ei hto;

hydroigide for hringin'g the ca with the cellulose. As

alcchm as elite a; trlh e'rol he r'nployed theac'jeta glycerol formed-m me 2. effect upon the care h I L am l -514@Zlfl.12f fitte s-A' quain- .t c ,ab.,.. h titative illustration 'of one method of carrying $5 tlon bemg'cont'inue duiing'a'dditiono f a'ctatin'g' 11 mixture, and continued at temperature preferably not to exceed 25 C. until a sample v rithdrawn shows a solubility in alcohol-freechloroform, or other solubility characteristics depending upon the degree of acetylation desired.

The granular mass, still substantially conserving the morphological structure of the original starch, is then washed in water to neutral reaction, centrifugalized and dried at a comparatively low temperature.

Example III.-Acetation,of cellulose in textile form. One hundred parts by weight of a thin muslin of width and length desired is deprived of moisture until it is substantially anhydrous, and then uniformly impregnated in the cooled condition with a mixture of 100-200 parts anhydrous methanol containing dissolved therein 2% to 3% by weight of iodic acid in concentrated solution for a period of about 5 hours, the cloth being turned or otherwise agitated during the contacting period of catalyst with cellulose.

The preferable amount of methanol to use, and the treatment period of cloth with dissolved iodic acid will depend in a measure upon the weight and other physical characteristics, and the nature of the cloth being treated.

,At the expiration of the impregnation or dissemination period, the cloth is placed under pressure or liquid evaporated therefrom until the weight of the cloth has been reduced to under 130% of its original weight, when it is then placed under tension and immersed in a closed container containing 300-350 parts concentrated acetic anhydride and 50-200 parts methyl acetate, the temperature range being kept below'about 25 C. Or the cloth may be placed under tension during the period of contact of catalyst with cellulose.

When a sample of cloth removed and purified shows the physical characteristics of cellulose triacetate (maximum acetated normal cellulose or thereabouts), the cloth, still under tension, is treated to remove reactants in any suitable manner, and moisture removed therefrom, after which the tension is removed.

In addition to the application of tension during cellulose treatment, physical characteristics as luster may also be modified by passing the acetated cloth into or through a chamber containing volatile solvents, plasticizers or other modifying liquids'or solids in vapor' forin, whereby a degree of incipient gelatinization of'the acetated fibers is allowed to take place, in degree depending upon the effect desired, and being modified by the tautness of the fibers during said treatment.

In a modification of the process, also given for illustrative purposes only and with the understanding that the reactants and conditions may be considerably modified, still conserving the essence of this invention, a'cotton fabric is taken, or a cotton fabric containing a proportion of linen therein or a proportion of mercerized fabric therein, and which has been degummed by a usual kier boil and bleached to produce standard or normal cellulose ofhigh purity, has its free and combined moisture evaporated therefrom by passage through a suitably ventilated section of a tenter dryer having a temperature sufi'iciently elevated to extract substantially all the moisture therefrom, but insufficiently high to cause appreciable oxidation or decomposition of the cellulose.

When the moisture content of the fabric has been reduced below 1%, the dehydrated fabric, preferably after being allowed to cool, is passed through a bath comprising sufiicient anhydrous methanol containing a mixture of bromic and iodic acid catalyst to thoroughly impregnate the fabric. After a period of contactjbetween catalyst and fabric, liquid is removed bytpassage of the fabric between squeeze rolls, and the methanol content of the fabric then further reduced substantially below its, saturation point by passing the fabric through a further drier section, so adjusted as to temperature and length that a single passage of fabric therethrough reduces the methanol content in the fabric to between 10% and 30% and preferably to increase on the weight of the goods, and the acid content is approximately l /z% of theweight of the goods. While this impregnation to a satisfactory degree of cellulose with catalyst'is normally but a matter of a few minutes, yet more uniform results appear to be obtained where cellulose and catalyst are allowed to contact several hours before esterification is initiated. a

The evaporated methanol may be recovered from the drier and condensed.

The fabric is cooled by evaporation of methanol therefrom and is then fed through a solution containing parts concentrated acetic anhydride to 50 parts methyl acetate. It is then passed under tension over rollers in contact with a stream of air.

The acetylation is completed in air and the catalyst or its decomposition products removed from the acetated fiber as by evaporation usually in less than a half hour. The temperature of the bath does not require external thermal control as the rise in temperature is insufficient to degenerate the cellulose, and when the bath contains diluent equal to more than the weight of anhydride, the temperature rise of the bath is negligible.

The fabric is then fed into a washer and washed in water at a temperature not exceeding the esterification temperature. Ordinarily any residual reagents may be completely washed out within 10 minutes with water at a temperature of 15 to 25 C. The product is then in suitable condition for finishing as a'textile fabric.

If it is desired to further waterproof the fabric, it may be passed through a confined atmosphere containing a solvent for the cellulose acetate, or the solvent may be uniformly sprayed thereon, then passed through a heating chamber for solvent removal. This induces an incipient gelatinization of the exterior layers of acetated cellulose fabric, and more or less binds the fibers together by the agglutinatin'g action of the dissolved or softened acetate portion.

This invention permits the formation of yarns or textiles of various and contrasting colors or shades of dyeing or printing the cellulose fibers, yarns or fabrics with ordinary cotton'dyes which are unaffected by the steps in this invention (such as those which are set or developed, as-by acids), prior to esterification thereof, thereby eliminating or minimizing the need of special and expensive dyes ordinarily required for dyeing carbohydrate esters, especially organic esters of cellulose. An application Serial No. 351,913 relating to the art of esterification is co-pending.

What is claimed is: a

1. In the art of carbohydrate esterification, the steps which include forming bromine pentoxide in situ in said carbohydrate, acetylating said carbohydrate with bromine pentoxide therein, and stabilizing the bromine pentoxide by oxygen during progress of acetylation. y

2. Process foresterifying dried fibrous cellulose comprising'impregnating said cellulose'with an 13 oxyacid of a halogen of greater atomic weight than fluorine, said oxyacid containing at least three oxygen atoms dissolved in an aliphatic alcohol containing less than five carbon atoms, afterwards removing a portion of catalyst and alcohol, then esterifying with an esterifying aliphatic anhydride to be combined with the carbohydrate for ester formation, continuing said esterification until the degree of ester formation desired has been attained, then removing reactants therefrom and drying the cellulose ester.

3. Method of acetylating comprising impregnating substantially anhydrous cellulose with substantially anhydrous methanol containing bromic acid, allowing cellulose and bromic acid to contact for a period of time, removing a portion of the liquid by pressure, treating the impregnated cellulose with concentrated acetic anhydride to form bromine pentoxide by reaction with said anhydride, to form water by reaction with the methanol, and to form an acetic'ester by reaction with the cellulose, stabilizing the bromine pentoxide by contact with oxygen during acetylation, permitting said pentoxide to volatilize from the esters, then removing reactants and aliphatic ester, finally washing to neutrality and drying.

4. In the art of carbohydrate esterification, the steps which include impregnating carbohydrate with bromic acid in a neutral aliphatic alcohol, then dehydrating bromic acid to its corresponding anhydride, and acetylating carbohydrate with acetic anhydride.

5. Process for esterifying cellulose in fibrous condition and textile form in which all esteriflable components entering therein are substantially anhydrous and the acetated cellulose has fibrous appearance, toughness, flexibility and elasticity of the original cellulose used, comprising impregnating cellulose textile with an oxyacid of a halogen of greater atomic weight than fluorine dispersed in an aliphatic alcohol of relatively low molecular weight but susceptible to esterification to an ester which is a non-solvent of the fibrous cellulose acetate formed, removing a portion of alcohol and acid, then immersing said impregnated cellulose into acetic anhydride containing an aliphatic acetate of the aliphatic alcohol previously used, introducing air into acetating bath, continuing action of acetic anhydride on cellulose until the degree of ester formation desired has been attained, removing reactants, washing to neutrality and finally removing moisture therefrom.

14 6. Method of acetylating comprising drying cellulose until water content thereof is less than 1%, impregnating said cellulose with methanol having bromic acid dissolved therein, reducing by 5 evaporation the proportion of methanol content of the cellulose below its saturation point, then treating the moistened cellulose with an acetylating reagent.

7. In a process for acetating carbohydrate wherein all components entering therein are substantially anhydrous, the step comprising impregnating carbohydrate with an oxyacid of a halogen of greater atomic weight than fluorine dispersed in a monohydric aliphatic alcohol of less than five carbon atoms.

8. In a process for acetating cellulose wherein the components entering therein are substantially anhydrous, the step comprising activating said cellulose with bromic acid dissolved in methanol.

ANNETTE. HARRIS PRA'I'I.

Administratria: of the Estate of William. Beach Pratt, Deceased.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,018 Ruperti Dec. 22, 1937 2,221,184 Ellis -1 Nov. 12, 1940 2,170,024 Heckert Aug. 22, 1939 2,130,150 Nathanson Sept. 13, 1938 2,000,602 Malm et al. May 7, 1935 2,076,555 Fothergill Apr. 13, 1937 1,739,863 Rosenthal et al. Dec. 17, 1929 1,746,663 Leuchs Feb. 11, 1930 2,045,161 Mueller et al. June 23, 1934 2,064,384 Richter et a1 Dec. 15, 1936 1,236,578 Lindsay Aug. 14, 1917 1,823,350 Clarke Sept. 15, 1931 920,828 Cross May 4, 1909 2,010,607 Ruperti Aug, 6, 1935 1,678,626 Jaeger July 24, 1928 2,103,012 Muller et al Dec. 21, 1937 2,175,842 Koetschet Oct. 10', 1939 FOREIGN PATENTS Number Country Date 405,825 Great Britain Feb. 15, 1934 325,231 Great Britain Feb. 13, 1930 525,265 Great Britain Aug. 26, 1940 

